Field of Invention
The present invention relates to a micro-electro-mechanical system (MEMS) device, especially a MEMS device which includes a proof mass and a multi-dimensional spring structure connected to one or more anchors in a center area of the proof mass, for assisting a multi-dimensional movement of the proof mass.
Description of Related Art
MEMS devices are well-known devices nowadays, and one common application of the MEMS devices is to sense movements. FIG. 1 shows a prior art MEMS device 10 according to U.S. Pat. No. 8,459,114, wherein three proof masses 11, 12, and 13 are provided for three-dimensional movement sensing. The proof masses 11, 12, and 13 have different mass amounts and sizes, and therefore each dimension requires a different design to sense the movement; as a result, the overall structure is complicated. The anchors connecting the proof masses 11, 12, and 13 to a fixed end 14 are not all at a center area of the MEMS device 10; hence, stress resulting from the temperature variation in the manufacturing process or in the operation may cause a distortion of the structure to reduce accuracy of the MEMS device 10.
FIG. 2 shows another prior art MEMS device 20 according to U.S. Pat. No. 7,637,160. The proof mass 21 of the MEMS device 20 is connected to a substrate 23 by anchors 22 at two sides in the Y-direction. The MEMS device 20 is only capable of sensing in-plane movements (in X and Y directions, FIG. 2) parallel to the substrate 23. The MEMS device 20 can not sense a three-dimensional movement, and a distortion may still happen.
FIG. 3 shows another prior art MEMS device 30 according to U.S. Pat. No. 7,134,340 (the MEMS device 30 has a symmetrical structure and FIG. 3 shows a one-fourth partial view of the MEMS device 30). The proof mass 31 of the MEMS device 30 is connected to a substrate (no shown) through a linkage 32, a spring 33, and anchors 34. The linkage 32 is connected to the substrate through multiple anchors 34, in order to avoid deformation or distortion. The layout design to some extent reduces the problem of deformation or distortion, but it limits the movement of the proof mass 31 to a two-dimensional movement and increases the complexity of the manufacturing process.
In view of the above, the prior art MEMS devices either can not sense a three-dimensional movement, or can not sustain a large stress to cause a large offset. For solving the defects of the prior art, the present invention provides a MEMS device capable of sensing a multi-dimensional movement while having a small offset under a large stress.